Enantioselective
Carbon Stable Isotope Fractionation of Hexachlorocyclohexane during
Aerobic Biodegradation by <i>Sphingobium</i> spp.
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Abstract
Carbon
isotope fractionation was investigated for the biotransformation of
γ- and α- hexachlorocyclohexane (HCH) as well as enantiomers
of α-HCH using two aerobic bacterial strains: <i>Sphingobium
indicum</i> strain B90A and <i>Sphingobium japonicum</i> strain UT26. Carbon isotope enrichment factors (ε<sub>c</sub>) for γ-HCH (ε<sub>c</sub> = −1.5 ± 0.1‰
and −1.7 ± 0.2‰) and α-HCH (ε<sub>c</sub> = −1.0 ± 0.2‰ and −1.6 ± 0.3‰)
were similar for both aerobic strains, but lower in comparison with
previously reported values for anaerobic γ- and α-HCH
degradation. Isotope fractionation of α-HCH enantiomers was
higher for (+) α-HCH (ε<sub>c</sub> = −2.4 ±
0.8 ‰ and −3.3 ± 0.8 ‰) in comparison to
(−) α-HCH (ε<sub>c</sub> = −0.7 ± 0.2‰
and −1.0 ± 0.6‰). The microbial fractionation between
the α-HCH enantiomers was quantified by the Rayleigh equation
and enantiomeric fractionation factors (ε<sub>e</sub>) for <i>S. indicum</i> strain B90A and <i>S. japonicum</i> strain UT26 were −42 ± 16% and −22 ± 6%,
respectively. The extent and range of isomer and enantiomeric carbon
isotope fractionation of HCHs with <i>Sphingobium</i> spp.
suggests that aerobic biodegradation of HCHs can be monitored in situ
by compound-specific stable isotope analysis (CSIA) and enantiomer-specific
isotope analysis (ESIA). In addition, enantiomeric fractionation has
the potential as a complementary approach to CSIA and ESIA for assessing
the biodegradation of α-HCH at contaminated field sites
